The overall objective of the proposed research is to investigate the mechanism by which 80 S eukaryotic ribosomes are dissociated into 40 S and 60 S subunits in preparation for the initiation of protein synthesis. Recently, we have partially purified a ribosome dissociation factor from wheat germ and have shown that this factor is distinct from the known initiation factors from this species. Our immediate goal is to purify this factor to homogeneity and to investigate its physical properties. In order to precisely define the mechanism of action of the dissociation factor, we will initially investigate the interaction of this factor with 80 S ribosomes, with 40 S and 60 S ribosomal subunits and with the RNA and protein components of the ribosome. Secondly, we will attempt to quantitatively determine the effect of this factor on the equilibrium between the 80 S ribosome and the 40 S and 60 S ribosomal subunits by investigating the effect of the dissociation factor on the equilibrium constant, on the rate of dissociation of the ribosome and on the rate of association of ribosomal subunits. We will also seek to define the role of this factor in protein synthesis and to investigate its interaction with other component of the protein synthesizing system.